In order to connect two workpieces, e.g., tubular workpieces, to each other to form an angle of, for example, 90°, each workpiece can first be cut obliquely at an angle of 45° and subsequently welded together at the cut edges. For the welding operation, the cut edges should abut each other in as planar a manner as possible which is difficult, however, when the laser cutting beam is oriented perpendicularly relative to the surface of the workpiece surface during the cutting operation because warped cut faces can be produced during separation. In order to prevent this, during oblique laser beam cutting, the laser cutting beam and the supersonic cutting gas flow which supports the laser cutting is inclined at an angle relative to the surface of the workpiece, the so-called oblique cutting angle. If the oblique cutting angle varies during the cutting operation, a planar cut face can also be produced with an oblique cutting action on a tube so that, for example, welding the cut edges is substantially easier. The oblique cutting operation can be carried out not only on tubular workpieces but also on thick and plate-like workpieces in order to be able to more readily weld them together at the oblique cut edges, for example, which are formed during the oblique cutting operation.
However, the above-described oblique laser beam cutting operation has not yet been completely mastered, i.e., there are substantial advance rate reductions (at an oblique cutting angle of 45° of up to 70%) and substantial reductions in quality in comparison with conventional laser beam cutting with a laser cutting beam orientated perpendicularly relative to the workpiece surface. For example, the cut edges produced during the oblique laser beam cutting operation can have surface qualities which vary in accordance with the oblique cutting angle such that it is possible to observe a powerful burr formation at one cut edge and a rough surface structure at the other cut edge.
In the case of trepanning microholes in turbine blades, the article “Melt Expulsion by a Coaxial Gas Jet in Trepanning of CMSX-4 with Microsecond Nd:YAG Laser Radiation,” (Proceedings of the SPIE, Vol. 5063) discloses laterally displacing the laser cutting beam, which is orientated at an oblique angle (in this case, for a drilling operation) relative to the workpiece, and the supersonic cutting gas flow or the cutting gas nozzle, which is orientated parallel with the laser cutting beam, in order to position the dynamic pressure point or the high-pressure region of the supersonic cutting gas flow directly over the hole. In that manner, it is intended to prevent the gas pressure and the thickness of the hardened melt from varying periodically along the wall of the hole, as is the case with a coaxial orientation of the gas flow and the laser beam axis when the workpiece surface is arranged obliquely relative thereto. Due to the lateral displacement, those oscillations are intended to be prevented and an increased gas flow is intended to be achieved through the hole, to allow easier discharge of the melt at the lower side of the hole. In order to increase the size of a hole, which is obtained by trepanning, another hole is placed beside it with overlapping. Overlaps between the holes in the range between 50% and 80% having been found to be advantageous.